The invention relates to a Method for measuring fault locations in high frequency cables and lines.
Measuring fault locations is used, in order to measure the length of cables or to find defective positions in cables.
For this usually a short impulse is sent into the cable to be measured and then the running time, the level and the phase of the reflections of the impulse are measured and evaluated. Such a measurement is also called TDR measurement. However, for this quite complex vector network analyzer systems are necessary, which are quite unmanageable, heavy and therefore are rather used as laboratory instruments.
However, a further variant presents itself as an alternative, which is technically less complex, but requires quite some calculating performance. With this variant a frequency sweep is sent into the cable and the addition of the basic signal and the reflected signal is evaluated in complex calculations, so that a fault location is possible. This variant is also called FDR measurement. The FDR measurement makes use of the fact that frequency information can be converted into the time range by means of a Fourier's transformation (or Fast-Fourier's transformation).
A spectrum analyzer with integrated frequency generator developed by now into a small durable piece of equipment, which proved itself especially in mobile use, is exactly suitable for such an application.
Document U.S. Pat. No. 5,949,236 relates to a method for measuring fault locations in high frequency cables and lines by means of the use of a frequency domain reflectometer. An impedance compensation factor is applied on the measured signals, in order to correct cable impedances of the measuring cable.
The impedance compensation factor is determined by a measurement run with reference impedance. The use of a spectrum analyzer for measuring fault locations is not disclosed.
Document WO-A-00 29862 relates to a method for correcting frequency-dependent and length-dependent line impedances for FDR-measurements carried out on high-frequency cables, during which a compensation function to be applied to a certain cable length for the compensation of the determined impedance course is determined with the help of impedance values provided by the manufacturer.